in regard

Probably an elision of "in regard that".

in regard

1. (obsolete) since; because; inasmuch as; considering that; considering.

   I cannot say that I ever saw an adder, in regard there are none in these parts.

   • 1587, Thomas Kyd, The Spanish Tragedie:

     Yet, in regard they substance passeth his,
     ⁠And that iust guerdon may befall desert,<br?⁠To him we yeeld the armour of the prince.
     ⁠How likes don Balthazar of this deuice?

   • a. 1682, Thomas Browne, On Tobacco:

     That which comes fermented and dyed unto us affords no distinct account, in regard it is infected with a decoction or lixivium

• as, given that, seeing that; see also Thesaurus:because

• John A. Simpson and Edmund S. C. Weiner, editors (1989), “in regard”, in The Oxford English Dictionary, 2nd edition, Oxford: Clarendon Press, →ISBN.

• Gardiner, drearing