1 (archaic) dear; beloved; treasured.
2 (archaic) willing, glad
soon, gladly (commonly in the phrase 'as lief')
Depend upon it, sir, many a rich man dining tonight upon roast swan would as lief exchange his vittles for a plate of this cooked cheese! (Marcel Theroux, Strange Bodies)
He wants no boisterous notes of artificial passion: he would as lief the town-crier spoke his lines. (Michael Phelan, The Young Priest's Keepsake)
Lief should I rouse at mornings. And lief lie down of nights. (A E Houseman, Last Poems)
Lief began as 'lēof' in Old English and has since appeared in many literary classics, first as an adjective and then as an adverb. It got its big break in the epic poem 'Beowulf' as an adjective meaning 'dear' or 'beloved.' The adverb first appeared in the 13th century, and in 1390, it was used in John Gower’s collection of love stories, 'Confessio Amantis.' Since that time, it has graced the pages of works by William Makepeace Thackeray, Alfred Lord Tennyson, and D.H. Lawrence, among others. Today, the adjective is considered to be archaic and the adverb is used much less frequently than in days of yore. It still pops up now and then, however, in the phrases 'had as lief,' 'would as lief,' 'had liefer,' and 'would liefer.' (Merriam-Webster)
'dearly, gladly, willingly' (obsolete or archaic), c. 1250, from Middle English adjective lief 'esteemed, beloved, dear,' from Old English leof 'dear, valued, beloved, pleasant' (also as a noun, 'a beloved person, friend'), from Proto-Germanic leuba- (source also of Old Norse ljutr, Old Frisian liaf, Dutch lief, Old High German liob, German lieb, Gothic liufs 'dear, beloved'), from PIE root leubh- 'to care, desire, love.' Often with the dative and in personal constructions with have or would in expressions of choice or preference ("and yet, to say the truth, I had as lief have the foppery of freedom, as the morality of imprisonment", 'Measure for Measure'). I want and I'd love to are overworked and misused to fill the hole left in the language when I would lief faded in 17c. (Online Etymology Dictionary)