infiltration

Etymology

It is formed from English infiltrate + -ion as a noun of action,^[2][3][4][5] perhaps after French infiltration, recorded in French in the 16th century.^[2] The verb is formed from English in- + filtrate, perhaps after infiltrer (Paré, 16th century).^[2][3][4] Here filtrate comes from the past participle of Medieval Latin filtrō (“to filter”), from filtrum (“felt”),^[2][3] which is from Proto-West Germanic *filtiz.^[3] A Middle English infiltracioun (“knitting together”), used of bones and ligaments probably before 1425 in the Middle English Chauliac, was taken separately from Medieval Latin infiltrātiō.^[6][3]

Earliest recorded meaning

In physics and geology, the percolation of water or of minerals in solution: 1794, in R. Kirwan's Elements of Mineralogy.^[2] Etymonline dates this sense to 1796,^[3] and Dictionary.com to 1790–1800.^[5]

Semantic evolution

From 1830 (in Herschel) it was also the permeation of a substance with something, chiefly in pathology,^[2] and since 1853 the passing of fluids such as blood or fat into the tissues.^[2] Figurative use for ideas and influences passing into something is from 1840, in J. S. Mill,^[2][3] and the gradual penetration of one people into another from 1904.^[2] The military sense, the gradual or stealthy penetration of enemy lines by small numbers of troops, is recorded from 1930,^[2][3] with figurative use from 1940.^[2] Weekley (1921) noted that it had come into much use, after French, in military and political senses.^[7] Merriam-Webster also uses it for something that infiltrates, such as a fatty deposit or an injected anaesthetic.^[8]

Timeline

• 1794 – percolation of water or minerals in solution.^[2] Etymonline dates it to 1796.^[3]
• before 1812 – an infiltrated deposit.^[2]
• 1830 – the permeation of a substance with something.^[2]
• 1840 – figurative, of ideas and influences.^[2][3]
• 1853 – physiology, of blood or fat penetrating the tissues.^[2]
• 1904 – the gradual penetration of one people into another.^[2]
• 1930 – military, stealthy penetration of enemy lines.^[2][3]

Meanings

Noun

1. The secret entry of people into an organization, a territory or enemy lines, to gain information or influence: The police feared infiltration of the union by informers.^[8][2]
2. The passing of a liquid or gas into the pores of a solid; percolation: the infiltration of rainwater into the soil.^[8][2]
3. (medicine) The spread of a substance, such as blood, fat, cells or a drug, into body tissue, or the substance so deposited.^[8][2]
4. The gradual penetration of a people, or of ideas, into another group.^[2][8]

Word family

• infiltrative

Related words

• infiltrate
• filter
• filtrate
• filtration
• felt

References

1. ^ a b Wiktionary, the free dictionary, https://en.wiktionary.org
2. ^ a b c d e f g h i j k l m n o p q r s t u v Oxford English Dictionary Online (accessed March 2026), Oxford: Oxford University Press
3. ^ a b c d e f g h i j k Harper, Douglas. Online Etymology Dictionary, https://www.etymonline.com
4. ^ a b Shorter Oxford English Dictionary on Historical Principles (2002), 5th ed., ed. William R. Trumble and Angus Stevenson, Oxford: Oxford University Press
5. ^ a b Dictionary.com Unabridged (2016), based on the Random House Unabridged Dictionary, New York: Random House
6. ^ Kurath, Hans; Kuhn, Sherman M.; Lewis, Robert E., eds. (1952–2001), Middle English Dictionary, Ann Arbor: University of Michigan Press; online edition ed. Frances McSparran et al. (2000–2018)
7. ^ Weekley, Ernest (1921), An Etymological Dictionary of Modern English, London: John Murray
8. ^ a b c d e Merriam-Webster Unabridged Dictionary (2024), online ed., Springfield, Mass.: Merriam-Webster