variant of ad- before t: attend.
Dictionary.com Unabridged Based on the Random House Unabridged Dictionary, © Random House, Inc. 2019
assimilated form of ad- "to, toward, before" before stems beginning in -t-; see ad-.
Online Etymology Dictionary, © 2010 Douglas Harper
The American Heritage® Stedman's Medical Dictionary Copyright © 2002, 2001, 1995 by Houghton Mifflin Company. Published by Houghton Mifflin Company.