From en.wiktionary.org:
** English
*** Etymology
From [en].
*** Verb
[en-verb]
1. [en] To increase the tonicity of a solution
2. * {{ quote-book | en | year=2010 | author= | title=Formulation and Process Development Strategies for Manufacturing Biopharmaceuticals | isbn=0470118121 | page=168 | url=https://books.google.com/books?id=gNUltOoceOQC&&pg=PA168
|passage=The study consisted of a screening design evaluating protein, buffer,
TONICIFYING agent, cryoprotectant, surfactant, and pH levels.}}
1. * {{ quote-book | en | year=2013 | author= | title=Multiple Sclerosis | isbn=1481660535 | page=438 | url=https://books.google.com/books?id=uK1Kod9BnssC&&pg=PA438
|passage=A non-ionic TONICIFYING agent is incorporated into the pharmaceutical
compositions to render the compositions isotonic[, where the TONICIFYING agent
is a carbohydrate].}}