どうも

どうも is a versatile word with three distinct functions: casual greeting/thanks, emphasis, and expressing vague uncertainty.

USAGE (greeting, thanks):
Used alone, どうも serves as a casual all-purpose greeting or thanks. It can mean "hi," "thanks," or "sorry" depending on context.

• どうも！: Hi! / Thanks!
• どうも、助(たす)かりました: Thanks, that helped.

USAGE (emphasis):
Strengthens apologies, thanks, and greetings:

• どうもありがとう: thank you very much
• どうもすみません: I'm very sorry
• どうも失礼(しつれい)しました: I'm very sorry for being rude

USAGE (somehow, it seems):
Expresses a vague feeling or impression — "somehow," "for some reason":

• どうも変(へん)だ: something seems off
• どうもうまくいかない: somehow it's not going well
• どうも彼(かれ)は嘘(うそ)をついているようだ: it seems like he's lying

USAGE (with a negative):
どうも〜ない is a very common frame meaning "just can't (quite)" — the speaker is trying but not succeeding, and cannot say why:

• どうも思(おも)い出(だ)せない: I just can't remember
• どうも納得(なっとく)できない: I just can't accept it

This is the same uncertainty sense above, not a separate meaning.

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どうも alone as a greeting is casual. Combined with ありがとうございます or すみません, it is appropriate in polite contexts.