لب doesn't appear in Hans Wehr's Modern Standard Arabic dictionary, but Lane's Arabic-English Lexicon has 3 entries for it, distinguished by diacritics. Select one below for the full classical Arabic definition.

• لَبڤبَ Form 1

  1 لَبڤبَ [لَبَّ, originally لَبِبَ,] sec. per. لَبِبْتَ, (S, K,) the most common form of the verb, (TA,) and [لَبَّ, originally لَبُبَ, like حَبَّ, originally حَبُبَ, q. v.,] sec. pers. لَبُبْتَ, aor. يَلَبُّ, (S, K,) in…

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• لَبٌّ

  لَبٌّ ذ inf. n. of لَبَّ “ he remained, &c. ” -b2- لبَّيْكَ [At thy service! lit., Doubly at thy service!] (S, K, &c.) and لَبَّيْهِ [At his service: &c.]. (TA.) [See an ex. voce مَرْهُوبٌ. It is used in the present day …

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• لُبٌّ

  لُبٌّ ذ (S, K) and (Msb) of a nut, an almond, and the like, What is in the inside; (S;) the heart, or kernel: (K:) of a palm-tree, the heart, or pith, called قَلْبٌ or قُلْبٌ. (S, K.) Pl. of the former لُبُوبٌ. (S.) -b2-…

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