It is an interesting word...
OED:
(i) Resembling a pill or pills;
(ii) very small;
(iii) covered in small, pill-shaped markings.
The word appears to have been coined by George Eliot in 1871 to mean (i) "Resembling a pill or pills;",
(i.e. small and spherical)
1871 ‘G. Eliot’ Middlemarch (1872) I. i. ii. 29 Has any one ever pinched into its pilulous smallness the cobweb of pre-matrimonial acquaintanceship?
but has been used since in the 1905 meaning of (ii) very small
(i.e. the size of pills.)
1905 Athenæum 1 July 7/2 Literature is made to descend on them in a gracious rain of pilulous duodecimos. [duodecimos is a size of paper approx. 7 inches high, and 4.5 inches wide.]
It seems then to have disappeared and reappeared in 1987 in the meaning of (iii) covered in small, pill-shaped markings.
1987
Antiquaries Jrnl. 67 267 Various amounts of pilulous slag, charcoal, incompletely reacted ore and occasionally fuel-ash slag..cling to this free surface.
(Red font = my additions.)