A Grammatical Dictionary of Botanical Latin

Palmus,-i (s.m.II), abl. sg. palmo: the palm of the hand; a Roman or English span, i.e. nine inches; also twelve digits; (in fungi) “the breadth of the four fingers appressed to each other = three Parisian ‘unciae’ = 2.91 inches = 7.39 cm (Linnaeus, 1770)” (S&D); cf. spithama,-ae (s.f.I), q.v.; cf. palma,-ae (s.f.I), the palm of the hand; see ‘span.’

NOTE: a digitus is 3/4 of an inch; twelve of them would equal 9 inches, or a span.

NOTE: palma,-ae (s.f.I): width of 3 inches [8 cm.]; “three inches, or the breadth of the four fingers [digitus,-i (s.m.II, = 3/4 inch) of the hand” (Lindley);

NOTE: a span is “an English unit of length based on [a] distance equal to 9 inches” (WIII); see span.

NOTE: there is a difference between the English and Latin words (palmus; dodrans) representing a span (nine inches) and the Greek word (spithama) which represents seven inches.

A digitus,-i (s.m.II), q.v., is 3/4 of an inch; twelve of them would equal 9 inches, or a Roman span: the palmus,-i (s.m.II) and dodrans,-antis (adj.part.B).