Other forms: sidling, sidles
To sidle is to move sideways in a shy or furtive way. Sidle up to somebody, sidle away, sidled over.
The sideways movement is what makes it look shifty: sidling up to somebody is approaching without facing them squarely, which is why the word carries a hint of not wanting to be noticed. Sidle up and sidle away are the usual pairs. Note that sidle was probably made backwards from sideling, an old word meaning sideways, which was mistaken for a participle.
1verbsidleTo move sideways in a shy or furtive way.
“The boy sidled towards the cake table when he thought nobody was looking.”
sidle is a sideways movement.
Sidle is probably a back-formation from sideling, an old adverb meaning sideways, read as though it were a present participle. English does this often enough — burgle, edit, donate.
The verb is from side + le, possibly a a back-formation from sideling, treating that word as the present participle of sidle. The noun is derived from the verb.
Etymology from Wiktionary, CC BY-SA
Practised in A Song of Ice and Fire