Learn how to say Underlayer correctly in English with this tutorial pronunciation video.
Oxford dictionary definition of the word underlay:
(past and past participle underlaid) [with object]
place something under (something else), especially to support or raise it:
the green fields are underlaid with limestone
the synth arpeggios start, underlaid by a lovely theme on bass
1something placed under or behind something else, especially material laid under a carpet for protection or support:
providing the proper underlay gives the carpet extra life
a polka-dot skirt with net underlay
2 Music the manner in which the words are fitted to the notes of a piece of vocal music.
Old English underlecgan (see under-, lay1)