Answer: upon

AnswerCrossword Clue
UPONImmediately after
UPONAt the moment of
UPONHaving studied
UPONApprised of
UPONWell versed in
UPONAbreast of
UPONResting atop
UPON"Once .. a midnight dreary..."
UPON"... my word!"
UPONBerwick-...-Tweed, England
UPONConversant about
UPONShortly after
UPONVery soon after
UPON"Once ....."
UPON"When You Wish .. a Star"
UPONInformed about
UPONIt often comes after once
UPONOn top of
UPON"Once .. a time ..."
UPONKnowledgeable about
uponon
UPONSecond word in many fairy tales
UPONAt the high point of
UPONAtop
UPONCovering
UPONFairy tale's second word
UPONSecond word in a fairy tale
UPONStraddling
UPON"It came ... a midnight.."
UPONOnce ... a time
UPONOver
UPONAfter "once"
UPONRiding, say
UPON"Once ... a midnight dreary"
UPONPreposition in British place names
UPON"Once .. a time..."
UPON".. my word!"
UPONSavvy about
UPONAt the top of
UPONTopping