Verb
(transitive) To make (more) dense.
Some space missions cool the propellant to almost freezing to densify it, so they can fit more fuel and oxidizer in the tanks.
(intransitive) To become (more) dense.
Source: en.wiktionary.orgI think water transport will see a revival. However, we're not going to replay the 20th century. The industrial city of that era will not be revived. Our cities are going to contract. Many of them will contract as a whole but densify at their core. James Howard Kunstler