A propos—To the point; seasonably; in due time. Fr.
A propos de bottes—By-the-bye. Fr.
A proverb is good sense brought to a point. John Morley.
A proverb is much matter decocted into few words. Fuller.
Apt alliteration's artful aid. Churchill. 10
Apt to revolt, and willing to rebel, / And never are contented when they're well. Defoe.
A puñadas entran las buenas hadas—Good luck pushes its way (lit. gets on) by elbowing. Sp. Pr.
A purpose you impart is no longer your own. Goethe.
A quatre épingles—With four pins, i.e., done up like a dandy. Fr.
Aquel pierde venta que no tiene que venda—He 15 who has nothing to sell loses his market. Sp. Pr.