Rashi on Exodus 18:8/רש"י על שמות י״ח:ח׳

1ויספר משה לחתנו AND MOSES RELATED TO HIS FATHER-IN-LAW [ALL THAT THE LORD HAD DONE] — in order to allure his heart that he might attach him to the Torah (Mekhilta).

2את כל התלאה ALL THE TRAVAIL that they had experienced at the Red Sea, and that caused by Amalek (Mekhilta).

3התלאה — The ל and א are part of the primary form of the word and the ת is a formative letter and a part of the primary form of the noun which sometimes is omitted from it. Similar examples are תרומה and תנופה and תקומה and תנואה.