The goddess Thetis and her sister Nereids, as the family of Achilles, are lamenting Achilles: presumably, their singing can be described as góos ‘lament’, as I infer by comparing the use of this word in referring to the laments performed by Hector’s family at I.24.723 / I.24.747 (also at I.24.760) / I. 24.761. In the case of Hector’s funeral, there are also laments performed by non-family professionals, I.24.720–722: these professionals are aoidoi ‘singers’ who are men, I.24.720, and they perform thrēnoi ‘laments’, I.24.721; as they perform, the word that refers to their performance is thrēneîn ‘make lament’, I.24.722, which is a verb derived from the noun thrēnos ‘lament’. So also here at O.24.61, we see the same verb thrēneîn ‘make lament’ applied to the singing of laments by the Muses themselves, who are in this context “professionals” by contrast with the Nereids, who are “family.” The lamenting of Achilles by the Muses is also described in Pindar Isthmian 8.56–60.