1A polite expression for asking 'how' or 'how about' — used to inquire about condition, opinion, or suggestion.
お茶はいかがですか？
Would you like some tea?
この案はいかがでしょうか？
How about this proposal?
体の具合はいかがですか？
How is your health?
2Mostly used in the pattern 'いかがなものか' to gently express doubt or disapproval about something — roughly "questionable" or "ill-advised."
会議中にスマホをいじるのはいかがなものか。
Fiddling with your phone during a meeting — is that really appropriate?
その決定はいかがなものかという声も上がっている。
Some voices are questioning whether that decision was wise.