The 20-year-old joins the League Two promotion-chasers on an initial one-month deal and could be in contention to face Bradford on Saturday if Football League clearance is granted in time.
The spell in Devon will be the youngster's second temporary move of the season after spending time at Cheltenham earlier in the campaign.
D'Ath only made three appearances for the Robins after picking up a knee injury in just his second start but did manage to score on his debut gainst Exeter.
The central midfielder also spent a large chunk of last season on loan at Yeovil and will add a welcome alternative for Grecians boss Paul Tisdale, who has seen Matt Oakley and Liam Sercombe ruled out in recent weeks.
