A smiley is a little round face drawn to show a feeling. Two dots and a curve, usually yellow.
The classic smiley is that yellow circle with a grin, born as a badge in the 1960s and everywhere by the 1990s. On a keyboard people typed one sideways and called that a smiley too. Today the word overlaps with emoji, though emoji covers every little picture and smiley covers the faces. As an adjective it simply means smiling a lot: a smiley child, a smiley receptionist, which in British English is a compliment.
Proto-Indo-European
*(s)mey-
Proto-Indo-European
*smey- — to laugh, be glad, wonder
Proto-Germanic
*smilāną — to smile
Proto-West Germanic
*smilēn
Old High German
smielēn
Middle High German
smielen
Middle Low German
*smîlen — to smile
Middle English
smilen — to smile
English
smile
English, today
smiley
From smile + y. The noun is from the adjective, after smiley face. smile comes from Middle English smilen (“to smile”), from Middle Low German smîlen (“to smile”), from Middle High German smielen, from Old High German smielēn, from Proto-West Germanic smilēn, from Proto-Germanic smilāną (“to smile”), from Proto-Indo-European smey- (“to laugh, be glad, wonder”). Cognate with Danish smile, Swedish smila, Faroese smíla (“to smile”); also stq smielje (“to smile”), Low German smielen (“to smile”), Dutch smuilen (“to smile”), Middle High German smielen (“to smile”). Related also to Old High German smierōn (“to smile”), Old English smerian (“to laugh at”), Old English smercian, smearcian "to smile"; > English smirk, Latin mīror (“to wonder at”).
Etymology from Wiktionary, CC BY-SA