Definition of "erst"

erst¹

/ɝst/

adjective
not comparable
1. (obsolete) First.

erst²

/ɝst/

adverb
not comparable
1. (obsolete) First of all, before (some other specified thing).
  Quotations
  Consider what I erst have been and what thou seest me now:
  1567, Arthur Golding, Ovid's Metamorphoses, book 2, line 691
2. (obsolete) Sooner (than); before.
  Quotations
  Thenne he sente the varlet ageyne and bad hym telle Kyng Mark that I wille come as soone as I am hole / for erste I maye doo hym noo good"Then he sent the varlet again, and bade him: Tell King Mark that I will come as soon as I am whole, for erst I may do him no good. "(please add an English translation of this quotation)
  1485, Sir Thomas Malory, “xxviij”, in Le Morte Darthur, book X
3. (archaic, poetic) Formerly, once, erstwhile.
  Quotations
  When lofty trees I see barren of leavesWhich erst from heat did canopy the herd
  1609, William Shakespeare, “Sonnet 12”, in Shake-speares Sonnets. […], London: By G[eorge] Eld for T[homas] T[horpe] and are to be sold by William Aspley