Sidle

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late 17th century: back-formation from sideling (see sidelong).

wiktionary

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The verb is from side +‎ -le( frequentative suffix), possibly a back-formation from sideling(“in a sidelong direction; askew, obliquely”, adverb), treating that word as the present participle of sidle. [1]

The noun is derived from the verb. [2]

etymonline

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sidle (v.)

"to move or go sideways," 1690s, back-formation from obsolete Middle English sidlyng (adv.) "obliquely, sideways; aslant; laterally" (early 14c., perhaps in Old English), from side (n.) + adverbial suffix -ling; altered on analogy of verbs ending in -le. Related: Sidled; sidling. Old English had sidlingweg (n.) "sidelong-way, oblique road."