Synonyms of 'fall behind'
▷ See fall
1 lagDictionary, trail, be left behind
The horse fell behind on the final furlong.
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The boys crept forward, Roger lagging a little.
If someone trails somewhere, they move there slowly, without any energy or enthusiasm, often following someone else.
I spent a long afternoon trailing behind him.
Thesaurus for fall behind from the Collins English Thesaurus
If you fall behind , you do not make progress or move forward as fast as other people.