A tilde is a symbol that is written over the letter 'n' in Spanish (ñ) and the letters 'o' (õ) and 'a' (ã) in Portuguese to indicate the way in which they should be pronounced.
tilde in British English
(ˈtɪldə)
noun
the diacritical mark (~) placed over a letter to indicate a palatal nasal consonant, as in Spanish señor. This symbol is also used in the International Phonetic Alphabet to represent any nasalized vowel
Word origin
C19: from Spanish, from Latin titulus title, superscription
tilde in American English
(ˈtɪldə)
noun
1.
a mark (˜) used:
a.
in Spanish, over an n to indicate a palatal nasal sound (ny), as in señor
b.
in Portuguese, over a vowel or the first vowel of a diphthong to indicate nasalization, as in lã, pão
2.
a similar mark used in some phonetic systems, to express negation in mathematics or logic, etc.
Word origin
Sp, metathetic var. of *title < L titulus, superscription, title