Not a word that foreign students of Spanish are likely to learn, but one with various meanings, is púa:
a sharp point, a barb;
a tooth of a comb;
a prickle, spine, or thorn of a plant;
a graft in a tree;
a plectrum or pick for a stringed instrument;
a phonograph needle;
the barb in barbed wire (alambre de púas).
Spanish púa developed from Vulgar Latin *pugia, which arose as a variant of the classical Latin noun pugio, with stem pugion-, that meant ‘a short weapon for stabbing, a dagger.’ The underlying Indo-European root is *peuk- ‘to prick,’ which also gave rise to the Latin noun pugnus ‘a fist’ that evolved to the synonymous Spanish puño. From that came puñal, which means the same as Latin pugio.
And where, you ask, is a connection to English? One that’s easy to see is pugilist, from Latin pugil ‘a person who fights with his fists, a boxer.’ Spanish retains the original as púgil, which English hasn’t borrowed, and also has pugilista. Both languages have the corresponding abstract noun pugilismo/pugilism. Both languages also share pugnaz/pugnacious, and Spanish has the verb pugnar ‘to fight, struggle.’ The Spanish compound repugnar ‘to oppose’ has its counterpart in English repugn, though the adjective repugnante/repugnant is more common.
© 2013 Steven Schwartzman