- The movable joint of the forceps of the lobster, crawfish, or crab; a dactylopodite.
- In <em>anatomy</em>, the innermost digit of the hand or foot, when there are five; the thumb or the great toe, especially the thumb, the great toe being usually distinguished as <em>pollex pedis</em>, or <em>hallux.</em>
- In <em>zoology</em>: The innermost digit of the fore limb only, when there are five; the digit that corresponds to the human thumb.
- The thumb of a bird; the short digit bearing the alula or bastard wing, regarded as homologous with either the human thumb or the forefinger.
- The first, or preaxial, digit of the fore limb, corresponding to the hallux in the hind limb; the thumb. In birds, the pollex is the joint which bears the bastard wing.
- The <xref>first</xref>, or <xref>preaxial</xref>, <xref>digit</xref> of the <xref>forelimb</xref>, corresponding to the <xref>hallux</xref> in the <xref>hind</xref> <xref>limb</xref>; the <xref>thumb</xref>. In birds, the pollex is the <xref>joint</xref> which bears the <xref>bastard wing</xref>.
- the thick short innermost digit of the forelimb