English
skydip
From sky + dip.
Proto-Germanic *skiwô ‘cloud cover, haze’
Proto-Germanic *skiwją ‘cloud; sky’
Old Norse ský ‘cloud; (plural) sky’
Middle English sky ‘sky; cloud’
English sky
Proto-Indo-European *dʰewbʰ- ‘to sink in’
Proto-Germanic *dupjaną
Proto-West Germanic *duppjan
Old English dyppan ‘to dip’
Middle English dippen
English dip
Today it means
noun Any of a series of measurements of atmospheric opacity taken using a telescope that dips from a high to a low elevation
Language periods are conventional ranges, not dates for this word.
Etymograph / skydip