どうも

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

AS GREETING/THANKS (casual):

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.

AS EMPHASIZER:

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

AS UNCERTAINTY MARKER:

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

REGISTER:
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.