Tímaguðsefni (titanium), léttjerni, forguðaglit or korneskaefni

 1) Tímaguðsefni

The name "titanium" was given by Martin Klaproth, in accordance with his views on chemical nomenclature in the counter-flow of the French chemical school, where they tried to name the element by its chemical properties. Since the German researcher himself noted the impossibility of determining the properties of a new element only by its oxide, he chose a name for it from mythology, by analogy with uranium that he had previously discovered.  

It is, therefore, reasonable to base the Icelandic on the international word.  Because there's no Icelandic word for this name of deities, and a translation of the German "Himmerstürmer" with addition of "-efni" would generate a word that is way to long.  An alternative way is naming the element after the leader of the Titans, Kronos, the god of time. This results into the word "Tímaguðsefni", of which the first two characters coincidentially are the same as the element's symbol.  

2) Léttjerni

Titanium is well known for its combination of lightness and strenght and is used iron-alloys.  It is a member of the so-called "iron-group of transition metals".  I propose the ending -jerni for these elements.  Some might say that "-jerni" sounds like a member of the "ferromagnetic triad" (iron, cobalt and nickel). But that depends which word you suffix.  The construction "léttjerni" suggest something that is lighter than iron, so this metal can't belong to the ferromagnetic triad.  Using "léttjerni" for iron consisting of the lightest stable isotop would be terminological illogical. Scandium is often excluded form the "iron-group of transition metals because it belongs to the "rare-earth elements". For that reason "léttjerni" could be used for titanium.

3) Forguðaglit

The Titans were the 12 Gods that preceded the 12 Olympians and have become a symbol for "the elder gods", the predecessing family of Gods: Fornguða- or Forguða- + glit (metallic lustre): Forguðaglit

4) Korneskaefni (Cornium)

Named after Cornwalls, because that's where titanium was discovered. Many elements are named after the countries or regions, where they were discovered, in this case "Cornwalls".