thaddha : [adj.] hard; stiff; callous.

A.P. Buddhadatta Mahathera, Concise Pali-English and English-Pali Dictionary [available as digital version from Metta Net, Sri Lanka]

Thaddha [pp. of thambeti, Sk. stabhnāti to make firm, prop, hold up; cp. Av. stawra firm, Gr. a)stemfh/s, stafulh/; Goth. stafs, Ags. staef=E. staff; Ohg. stab. See also khambha & chambheti] 1. lit. hard, rigid, firm J i.293 (opp. muduka); Vism 351 (˚lakkhaṇa); PvA 139 (=ujjhangala). -- 2. fig. (a) hardened, obdurate, callous, selfish D i.118 (māna˚); iii.45 (+atimānin); A ii.26=It 113 (kuha th. lapa); Sn 104 (see gotta˚); J i.88 (māna˚) ii.136; Sdhp 90. -- (b) slow Miln 103 (opp. lahuka; cp. BSk. dhandha, on which Kern, Toev. ii.90). -- See thambha & thūṇa.
   -- maccharin obdurate & selfish, or very selfish DhA iii.313; VvA 69; PvA 45; -- hadaya hard -- hearted J iii.68.

Pali-English Dictionary, TW Rhys Davids, William Stede,