PAL

Ptolemaeus Arabus et Latinus

_ (the underscore) is the placeholder for exactly one character.
% (the percent sign) is the placeholder for no, one or more than one character.
%% (two percent signs) is the placeholder for no, one or more than one character, but not for blank space (so that a search ends at word boundaries).

At the beginning and at the end, these placeholders are superfluous.

centre ‘centre’

French

References: Alm. Toomer: 41. – PH Morelon: I.3:1, 18:6
Translation of:
Greek: κέντρον [Alm. Heiberg: I.5, 17:2. – PH Heiberg: I.3:1, 74:5]
Arabic: مركز [Alm. MS Tunis: . – PH Morelon: I.3:1, 19:4]