This rare kanji has no clear standalone meaning. Treat its meaning as uncertain.
The exact historical development of 躵 is uncertain. It combines 身 (body) with 忍 (endure, conceal), but whether this is a phono-semantic compound or a later formation is unclear.
With 身 (body) and 忍 (endure, conceal), imagine a body concealing itself to endure a situation, perhaps aiming or bearing something silently.
For ねらう, picture a ninja (忍者, にんじゃ) aiming at a target while enduring hardship: the ninja's endurance (忍) and body (身) combine to ねらう (aim).
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