In a game of Codenames, Team 1 field operative guesses a wrong choice for a word. During or before their next turn they say, "oh, I know which one you meant for last code".
Would that be against the rules?
Field Operatives are only allowed to discuss the clue after their Spymaster provides it, until their team's turn is over.
Rules, P.4 "MAKING CONTACT
When the spymaster gives a clue, his or her field operatives try to figure out what it means. They can debate it amongst themselves..."
Same page: "Number of Guesses
...Any wrong guess ends the turn immediately..."
This is reiterated and summarized on page 5: "GAME FLOW
Spymasters take turns giving clues. After a spymaster gives a clue, his or her team starts guessing. Their turn ends when they guess wrong, when they decide to stop, or when they have made the maximum number of guesses for that clue. Then it is the other team's turn"
Any other discussion of a previous clue, during another team's turn or on an operative's own turn prior to the new clue being read, is therefore out of scope of the rules (i.e., it's not allowed). This conveniently addresses any clue-related discussion among the operatives, but also any directed towards the spymaster (whether or not it is acknowledged by the spymaster). This would apply equally to basically harmless and vague discussion like "Oh, I know what you meant now" or, taken to its logical conclusion, a field operative explicitly instructing their spymaster to add 1 to the number of guesses on their new clue (effectively providing +2 potential guesses).
So if you're a field operative, unless you want to talk about getting snacks for the table when it isn't your turn or before your team's clue is read, don't say anything!
No, that is not allowed.
Looking at rules here they say :-
If you are a field operative, you should focus on the table when you are making your guesses. Do not make eye contact with the spymaster while you are guessing. This will help you avoid nonverbal cues. When your information is strictly limited to what can be conveyed with one word and one number, you are playing in the spirit of the game.
Communication such as "oh, I know which one you meant for last code" Is not in that spirit. Doing so risks a reaction from the spymaster. Just as the spymaster can not say "that one is right but its not what I meant".
Once they game is over then its fun to discuss what was meant/misinterpreted by the clues but this is can not be alluded to during the game its self.
Yes. The communication flow is limited from the Spymaster to the Field Operative, communication from the Field Operative to the Spymaster is not limited. The Spymaster, however, cannot react to it.
The quote from the other answer is part of "Keeping a Straight Face", directed to the Spymaster. The full quote is:
The spymaster is expected to keep a straight face. Do not reach for any card while your teammates are considering the words. When a teammate touches a word, consult the key card and cover the word with the card of the corresponding color. When a teammate chooses a word of the correct color, you should act as though it was exactly the word you meant, even if it wasn't.
If you are a field operative, you should focus on the table when you are making your guesses. Do not make eye contact with the spymaster while you are guessing. This will help you avoid nonverbal cues.
When your information is strictly limited to what can be conveyed with one word and one number, you are playing in the spirit of the game.
My highlights are to show that the intention is to avoid you picking up nonverbal cues from your Spymaster, not to avoid you communicating things to your Spymaster. You can say as much as you want, even talk your thought process out loud so the Spymaster can better give clues going forward (whatever you say can and will be used by your opponents to rule out words as not theirs too, so be careful).
See that the whole section is to avoid the Spymaster giving signs to the Field Operatives, not the other way around. Therefore, if a Field Operative says "oh, I know which one you meant for last code" the Spymaster cannot visibly/audibly react in any way, that would be against the spirit. But the Spymaster can know that so as to not give extra clues on that word.
See this part too:
When the spymaster gives a clue, his or her field operatives try to figure out what it means. They can debate it amongst themselves, but the spymaster must keep a straight face. The operatives indicate their official guess when one of them touches one of the codenames on the table.
The Field Operatives can and should communicate freely, even saying why they think a word is what and other things, their communication is explicitly not restricted. The Spymaster however should not react visibly/audibly to any of it.
It's a party game. This happens all the time and it's part of the emotions that make it fun. As long as the spymaster keeps the "straight face", no illegal information is given. The agents are allowed to openly discuss what they think so the spymaster already knows all this. Telling people off for getting excited about the game, does not make it more fun. We had some heated discussions about illegal clues and spymasters giving hints by reaching for a certain card while the agents are still debating, but saying "oh now I know" would not upset anyone.