せめて

せめて means "at least": you can't have what you really want, so you settle for something smaller. It goes in front of the smaller thing, and the sentence ends in a wish, a request or a regret – たい, てほしい, てください, ばよかった, のに.

The smaller thing often carries だけでも ("just this") or くらいは ("this much"), which lower the bar further.

With ば or たら and のに, せめて looks back at what would have been enough and regrets that it didn't happen.

せめて or 少なくとも

すくなく少なくとも is also "at least", but it states a minimum as a fact. せめて needs someone to want something, so a plain statement of what is the case takes 少なくとも.

• × せめて週に一回は運動している → 少なくとも週に一回は運動している