Noun
whole note (plural whole notes)
(Canada, US, music) A semibreve, a musical note four beats long in 4/4 time.
A "third note" would be one third of a whole note, and thus is a half-note triplet. Source: Internet
For example, where main implies a bar construction of four quarter-parts of a whole note (i. Source: Internet
Three half notes in the first measure (making up a dotted whole note) are equal in duration to two half notes in the second (making up a whole note). Source: Internet