From the SI prefix milli- (indicating a thousandth) + Helen, of Troy, the maiden so beautiful that her abduction by Paris sparked the Trojan War and was said, in Christopher Marlowe’s 1604 Tragical History of Doctor Faustus, to have ‘launched a thousand ships’.
millihelen (plural millihelens)
(informal) A unit of measure of pulchritude, corresponding to the amount of beauty required to launch one ship. [quotations ▼]
According to Raymond Augustine Bauer and Kenneth J. Gergen (The Study of Policy Formation, 1968), ‘one could also speak of fractional millihelens, say, enough beauty to launch two cabin boys’.millihelen - Wiktionary